1. Field of the Invention
The present invention relates to a motor driving device for driving a motor, and a motor unit in which the driving device is integrated with the motor. In particular, the invention relates to a motor driving device and a motor unit that are driven by a pulse-width-modulated power supply voltage.
2. Description of the Related Art
An information processing device such as a PC (personal computer) is provided with fans for cooling the inner portion of the device. Further, there is a fan of which the number of revolutions is changed according to the operational state of the device. For example, there is a fan of which the number of revolutions of a fan motor is changed according to the temperature of a heating element in order to improve cooling performance and reduce noise in a PC.
FIG. 6 is a view showing the configuration of a driving circuit of a fan motor in the related art.
In FIG. 6, a driving circuit of a single-phase full-wave brushless DC motor is shown as an example. The motor driving circuit includes a Hall element 11, a Hall amplifier 12, a waveform shaping circuit 13, a switching control circuit 14, and a power output circuit 16. Further, the power output circuit 16 includes pnp transistors Q1 and Q2 and npn transistors Q3 and Q4. Both ends of a coil L1 forming a stator of the motor are connected to a portion between the transistors Q1 and Q3 and a portion between the transistors Q2 and Q4, so that an H bridge circuit is formed.
In addition, the motor driving circuit is provided with a power terminal 41, a ground terminal 42, and an FG (Frequency Generator) output terminal 43. Further, the Hall element 11, the Hall amplifier 12, the waveform shaping circuit 13, the switching control circuit 14, and the power output circuit 16 are driven by a power supply voltage VCC that is commonly input from the power terminal 41.
The Hall element 11 is provided in the fan motor, and outputs a voltage signal corresponding to the direction of a magnetic field that is changed due to the rotation of the rotor 31 of the fan motor. The Hall amplifier 12 amplifies an output signal that is output from the Hall element 11. The waveform shaping circuit 13 shapes the waveform of the output signal, which is output from the Hall amplifier 12, in a pulse shape. Further, the waveform shaping circuit outputs an FG signal, which is used to detect the number of revolutions of the rotor 31, from the FG output terminal 43 to an external control device (not shown).
Furthermore, the output signal that is output from the Hall amplifier 12 is also sent to the switching control circuit 14. The switching control circuit 14 outputs a switching signal, which switches the switching operations of the transistors Q1 to Q4 of the power output circuit 16, on the basis of the output signal that is output from the Hall amplifier 12, and determines the direction of current flowing in the coil L1 so that the rotor 31 is rotated in a definite direction.
The above-mentioned motor driving circuit, the fan motor that includes the coil L1 and the rotor 31, and a fan 32 may be unitized as, for example, a fan motor unit 100. Further, as described below with reference to FIGS. 7 to 10, the rotational speed of the fan motor is changed by controlling the power supply voltage VCC applied to the motor driving circuit.
FIG. 7 is a view illustrating a first method of changing the rotational speed of the fan motor by using the motor driving circuit of FIG. 6. FIG. 8 is a graph showing the relationship between a control voltage and a power supply voltage when the method of FIG. 7 is used.
In this case, a transistor Q51 used to control the power supply voltage is provided outside the fan motor unit 100 shown in FIG. 6. The transistor Q51 is an npn transistor, a power supply voltage (herein, 12 V) used to perform an operation is applied to a collector, and an emitter is connected to the power terminal 41 of the fan motor unit 100. Further, a control voltage Vc, which is a DC voltage used to indicate the rotational speed of the fan motor, is applied to a base of the transistor Q51 from a control device (not shown). As shown in FIG. 8, if the control voltage Vc is changed, the power supply voltage VCC applied to the power terminal 41 of the fan motor unit 100 is changed, so that the rotational speed of the rotor 31 is changed according to the change of the power supply voltage.
Further, FIG. 9 is a view illustrating a second method of changing the rotational speed of the fan motor by using the motor driving circuit of FIG. 6, and FIG. 10 is a graph showing the change of a power supply voltage when the method of FIG. 9 is used.
The first method illustrated in FIG. 7 has a problem that power loss of the transistor Q51 provided outside the fan motor unit is large. Meanwhile, according to the example shown in FIG. 9, a pnp transistor Q52 instead of the transistor Q51 is provided outside the fan motor unit, and a PWM (Pulse Width Modulation) signal is input to a base of the transistor Q52 as a control voltage Vc. The transistor Q52 is switched according to the PWM signal, so that the waveform of the power supply voltage VCC applied to the fan motor unit 100 is formed in a pulse shape as shown in FIG. 10. Further, the pulse width of the power supply voltage VCC is also changed according to the change of the pulse width of the control voltage Vc, so that the effective voltage of the power supply voltage VCC is changed. Therefore, it may be possible to change the rotational speed of the rotor 31.
The above-mentioned method is generally used in the laptop computer in which power saving is particularly demanded. In particular, if the method is used in a system such as a fan motor of a laptop computer in which the rotational speed of a motor does not need to be finely controlled, it maybe possible to simplify the configuration of the circuit and to reduce manufacturing cost and the size of the circuit. Further, if a PWM signal is used, it may be possible to also obtain a merit that a digital circuit is easily controlled.
Next, FIG. 11 is a view showing another configuration of a driving circuit of a fan motor in the related art.
FIG. 11 shows the configuration of a so-called sensorless motor driving circuit that does not use a device for detecting the position of the rotor 31 such as a Hall element. Meanwhile, the sensorless motor driving circuit uses a three-phase brushless DC motor as a fan motor.
The motor driving circuit 200 includes a counter electromotive force detecting circuit 51, an FG detecting circuit 52, a timing generating circuit 53, a switching control circuit 54, a start logic circuit 55, a clock generating circuit 56, and power output circuits 57a to 57c. Further, a power terminal 71, a ground terminal 72, an FG output terminal 73, coil terminals 74a to 74c that correspond to a U phase, a V phase, and a W phase, respectively, and a common terminal 75 are provided as input/output terminals.
Each of the power output circuits 57a to 57c includes two switch elements (for example, a pnp transistor and an npn transistor), and a six-element bridge circuit is formed by the switch elements and the coils L11 to L13. That is, one ends of the corresponding coils L11 to L13 are connected to nodes between two switch elements of the power output circuits 57a to 57c through the coil terminals 74a to 74c, respectively, and the other ends of the coils L11 to L13 are commonly connected to the common terminal 75. Further, each of the power output circuits 57a to 57c is driven by the power supply voltage VCC that is applied from the power terminal 71.
The counter electromotive force detecting circuit 51 compares the voltages between the common terminal 75 and the coil terminals 74a to 74c with a predetermined voltage, in order to detect the polarities of the counter electromotive forces generated in the coils L11 to L13. The FG detecting circuit 52 converts the detection result of the counter electromotive force corresponding to each phase into position information. Further, the FG detecting circuit outputs an FG signal, which is used to detect the number of revolutions of the rotor 31, from the FG output terminal 73 to an external control device (not shown).
The timing generating circuit 53 performs a counting operation, which is based on the zero-cross timing of the voltage of each of the coils L11 to L13, on the basis of the detection result of the counter electromotive force detecting circuit 51. The timing generating circuit generates a timing signal that is used as reference of a conduction timing corresponding to each phase. The switching control circuit 54 switches the turning-on/off operation of each of the switch elements of the power output circuits 57a to 57c on the basis of the timing signal generated by the timing generating circuit 53, and allows current to selectively flow in the coils L11 to L13 so that the rotor 31 is rotated in a definite direction.
The start logic circuit 55 and the clock generating circuit 56 are circuits operated during the driving without a sufficient counter electromotive force. The start logic circuit 55 controls the timing generating circuit 53 so that the timing generating circuit generates a timing signal. The timing signal allows the rotor 31 to be rotated on the basis of the clock signal generated by the clock generating circuit 56. When the rotational speed of the rotor 31 reaches a predetermined rotational speed through the control of the start logic circuit 55, the operation of the start logic circuit 55 is stopped and switched into the control operation based on the detection result of the counter electromotive force detecting circuit 51.
Meanwhile, there has been the following device as a motor control device in the related art. The device has the configuration in which a switching element is provided on a power supply line of a DC fan motor and a PWM controlled is performed, and a capacitor that delays turning-off and has small capacitance is provided between a collector and a base of the switching element (bipolar transistor). Therefore, clicking sound is reduced during the switching-off (for example, see JP-A-2003-319677 (paragraph Nos. [0020] to [0023], FIG. 1)).
Further, there has been also a motor control device that controls the compensation of a motor driving unit on the basis of a voltage detection signal, which is obtained by dividing DC power supplied to a motor driving unit. The motor driving unit and a control unit thereof share ground terminals, and the voltage detection signal is directly sent to the control unit, so that an isolation amplifier does not need to be provided (for example, see JP-A-11-235088 (paragraph Nos. [0007] to [0009], FIG. 1)).
In addition, there has been the following control circuit of a brushless DC motor. The control circuit compares a voltage, which is obtained by converting current supplied to the DC motor, with a predetermined voltage, and counts the waveform output as the comparison result, thereby detecting the number of revolutions of the DC motor (for example, see JP-A-2006-180610 (paragraph Nos. [0017] to [0019], FIG. 1))